Acids and Bases 1
UNIT 4: ACIDS & BASES OUTCOMES All important vocabulary is in Italics and bold. Outline the historical development of acid base theories. Include: Arrhenius, BronstedLowry, Lewis. Write balanced acid/base chemical equations. Include: conjugate acid/base pairs, amphoteric behavior. Distinguish between strong and weak acids and bases. Include: electrolytes and nonelectrolytes Describe the relationship between the hydronium and hydroxide ion concentrations in water Include: the ion product of water, K w Formulate an operational definition of ph. Solve problems involving ph. Describe how an acidbase indicator works in terms of colour shifts and Le Chatelier s Principle. Write the equilibrium expression (K a or K b ) from a balanced chemical equation. Use K a or K b to solve problems for ph, percent dissociation and concentration. Predict whether an aqueous solution of a given ionic compound will be acidic, basic or neutral given the formula. Write balanced neutralization reactions involving strong acids and bases. Calculate the concentration or volume of an acid or base from the concentration and volume of an acid or base required for neutralization. Using a standardized acid or base, determine the concentration of an unknown base or acid. Additional KEY Terms monoprotic diprotic amphoteric salt hydrolysis concentrated dilute standard solution end point equivalence point titration Relative Strengths of Acids 2
*Acids 1.0 mol/l in water at 25ºC Acid Reaction K a Perchloric acid HClO 4 + H 2 O H 3 O + + ClO 4 very large Hydriodic acid HI + H 2 O H 3 O + + I very large Hydrobromic acid HBr + H 2 O H 3 O + + Br very large Hydrochloric acid HCl + H 2 O H 3 O + + Cl very large Nitric acid HNO 3 + H 2 O H 3 O + + NO 3 very large Sulfuric acid H 2 SO 4 + H 2 O H 3 O + + HSO 4 very large Oxalic acid H 2 C 2 O 4 + H 2 O H 3 O + + HC 2 O 4 5.4 x 10 2 Sulfurous acid H 2 SO 3 + H 2 O H 3 O + + HSO 3 1.7 x 10 2 Hydrogen sulfate ion HSO 4 + H 2 O H 3 O + + SO 42 1.3 x 10 2 Phosphoric acid H 3 PO 4 + H 2 O H 3 O + + H 2 PO 4 7.1 x 10 3 Ferric ion 3+ Fe(H 2 O) 6 + H 2 O H 3 O + + Fe(H 2 O) 5 (OH) 2+ 6.0 x 10 3 Hydrogen telluride H 2 Te + H 2 O H 3 O + + HTe 2.3 x 10 3 Hydrofluoric acid HF + H 2 O H 3 O + + F 6.7 x 10 4 Nitrous acid HNO 2 + H 2 O H 3 O + + NO 2 5.1 x 10 4 Hydrogen selenide H 2 Se + H 2 O H 3 O + + HSe 1.7 x 10 4 Chromic ion Cr(H 2 O) 3+ 6 + H 2 O H 3 O + + Cr(H 2 O) 5 (OH) 2+ 1.5 x 10 4 Benzoic acid C 6 H 5 COOH + H 2 O H 3 O + + C 6 H 5 COO 6.6 x 10 5 Hydrogen oxalate ion HC 2 O 4 + H 2 O H 3 O + + C 2 O 42 5.4 x 10 5 Acetic acid HC 2 H 3 O 2 + H 2 O H 3 O + + C 2 H 3 O 2 1.8 x 10 5 Aluminum ion Al(H 2 O) 3+ 6 + H 2 O H 3 O + + Al(H 2 O) 5 (OH) 2+ 1.4 x 10 5 Carbonic acid H 2 CO 3 + H 2 O H 3 O + + HCO 3 4.4 x 10 7 Hydrogen sulfide H 2 S + H 2 O H 3 O + + HS 1.0 x 10 7 Dihydrogen phosphate ion H 2 PO 4 + H 2 O H 3 O + + HPO 42 6.3 x 10 8 Hydrogen sulfite ion HSO 3 + H 2 O H 3 O + + SO 32 6.2 x 10 8 Ammonium ion + NH 4 + H 2 O H 3 O + + NH 3 5.7 x 10 10 Hydrogen carbonate ion HCO 3 + H 2 O H 3 O + + CO 32 4.7 x 10 11 Hydrogen telluride ion HTe + H 2 O H 3 O + + Te 2 1.0 x 10 11 Hydrogen peroxide H 2 O 2 + H 2 O H 3 O + + HO 2 2.4 x 10 12 Monohydrogen phosphate HPO 42 + H 2 O H 3 O + + PO 43 4.4 x 10 13 Hydrogen sulfide ion HS + H 2 O H 3 O + + S 2 1.2 x 10 15 Water H 2 O + H 2 O H 3 O + + OH 1.8 x 10 16 Hydroxide ion OH + H 2 O H 3 O + + O 2 < 10 36 Ammonia NH 3 + H 2 O H 3 O + + NH 2 very small POLYATOMIC IONS 3
NAME FORMULA CHARGE ACETATE CH 3 COO 1 AMMONIUM + NH 4 +1 HYDROGEN CARBONATE (BICARBONATE) HCO 3 1 CARBONATE 2 CO 3 2 CHLORATE ClO 3 1 CHLORITE ClO 2 1 CHROMATE 2 CrO 4 2 DICHROMATE 2 Cr 2 O 7 2 DIHYDROGEN PHOSPHATE H 2 PO 4 1 HYDROGEN PHOSPHATE 2 HPO 4 2 PHOSPHATE 3 PO 4 3 HYDROGEN SULFATE (BISULFATE) HSO 4 1 SULFATE 2 SO 4 2 HYDROGEN SULFITE (BISULFITE) HSO 3 1 SULFITE 2 SO 3 2 HYDRONIUM H 3 O + +1 HYDROXIDE OH 1 PERCHLORATE ClO 4 1 HYPOCHLORITE ClO (OCl ) 1 NITRATE NO 3 1 NITRITE NO 2 1 PERMANGANATE MnO 4 1 THIOCYANATE SCN 1 Patterns for Naming Polyatomic Ions ate ending is the general (base) form. The ending changes depending on the number of oxygen atoms notice the charge remains the same in these cases. ClO 3 chlorate base oxygen atoms ClO 4 perchlorate base + 1 oxygen atom ClO 2 chlorite base 1 oxygen atom ClO hypochlorite base 2 oxygen atoms 4
*FOLLOW THE MOVING HYDROGEN ION* 1. Identify the acid, base, conjugate acid and conjugate base for each of the following. a) HClO 4 (aq) + H 2 O (l) H 3 O + (aq) + ClO 4 (aq) b) H 2 SO 3 (aq) + H 2 O (l) H 3 O + (aq) + HSO 3 (aq) c) HC 2 H 3 O 2 (aq) + H 2 O (l) H 3 O + (aq) + C 2 H 3 O 2 (aq) d) H 2 S (g) + H 2 O (l) H 3 O + (aq) + HS (aq) e) HSO 3 (aq) + H 2 O (l) H 3 O + (aq) + SO 3 2 (aq) f) NH 3 (g) + H 2 O (l) NH 4 + (aq) + OH (aq) g) HF (aq) + HSO 3 (aq) F ( aq) + H 2 SO 3 (aq) h) HNO 2 (aq) + HS (aq) NO 2 (aq) + H 2 S (aq) 2. Predict which reactant will accept a hydrogen ion and complete the products for each equation. Label each reactant as an acid or base. List under the first reactant whether it falls under the Arrhenius (A) and/or BronstedLowry (BL) definition of an acids/bases E.g. HBr (aq) + H 2 O (l) H 3 O + (aq) + Br (aq) Acid Base (A and BL) a) HI (aq) + H 2 O (l) b) HF (aq) + H 2 O (l) c) H 2 CO 3 (g) + H 2 O (l) d) CO 3 2 (aq) + H 2 O (l) e) O 2 (aq ) + H 2 O (l) f) HSO 3 (aq) + H 2 O (l) 5
Write the dissociation of each of the following in water. Predict whether each of the following will be an electrolyte or nonelectrolyte. 1. NaOH (s) 2. Na 2 CO 3 (s) 3. Mg(OH) 2 (s) 4. C 6 H 12 O 6 (s) 5. HCl (g) 6. K 3 PO 4 (s) 7. H 2 SO 4 (aq) 8. NaC 2 H 3 O 2 (s) 9. (NH 4 ) 2 SO 4 (s) 10. C 2 H 5 OH (l) 11. H 3 PO 4 (aq) 12. CaCl 2 (s) 6
1. In each case: i. Complete the acidbase equation with the help of tables if needed. ii. ii. Label the acid, base, CA, CB. iii. Explain whether the reactants or products are favored at equilibrium. a) H 3 PO 4 + C 2 H 3 O 2 b) C 2 H 3 O 2 + HSO 4 c) SO 3 2 + NH 4 + d) HO 2 + H 2 CO 3 e) Al(H 2 O) 6 3+ + HSe 2. List the following in decreasing (strongest to weakest) order of strength as bases. a. CO 3 2 b. HCO 3 c. HPO 4 2 d. CH 3 COO e. HSO 3 3. List the following substances in increasing order (weakest to strongest) of strength as acids and bases. Some may be used more than once. F, H 2 PO 4, HSO 4, H 2 S, C 2 H 3 O 2, HNO 2, HTe 7
ANSWER THE FOLLOWING QUESTIONS ABOUT Kw AND ION CONCENTRATION: 1. What is the hydroxide ion concentration in a solution with an hydronium concentration of 6.80 10 10 mol/l? 2. What is the [H 3 O + ] in a solution with [OH ] of 5.67 10 3? 3. If the [H 3 O + ] in a nitric acid solution is 0.0020 mol/l, what is the [OH ]? 4. If the [OH ] in a sodium hydroxide solution is 0.050 mol/l, what is [H 3 O + ]? 5. 0.25 moles of hydrogen chloride gas is dissolved in 2.0 L of water. Write the dissociation equation for this gas and calculate both [H 3 O + ] and [OH ]. 6. 10.0 g of lithium hydroxide is dissolved in 750 ml of water. Write the dissociation equation and calculate both [H 3 O + ] and [OH ]. 7. 10.0 g of calcium hydroxide is dissolved in 400.0 ml of solution. Write the dissociation equation and calculate both [H 3 O + ] and [OH ]. 8. If the [H 3 O + ] of a barium hydroxide solution is 1.0 10 13 mol/l, calculate the [OH ]. How many grams of barium hydroxide must have been used to make a Litre of this solution? 9. Calculate the [H 3 O + ] in milk of magnesia (magnesium hydroxide) that has an [OH ] of 1.43 10 4 mol/l. Answer Key 1) 1.47 x 10 5 M, 2) 1.76 x 10 12 M, 3) 5.0 x 10 12 M, 4) 2.0 x 10 13 M, 5) 0.125 M, 8.0 x 10 14 M 6) 1.79 x 10 14 M, 0.559 M 7) 1.48 x 10 14 M, 0.675 M 8) 8.6 g, 9) 6.99 x 10 11 M 8
ANSWER THE FOLLOWING QUESTIONS ON ph and poh: 1. Determine the ph of each of the following values a. [H + ] = 1.0 x 10 6 b. [H + ] = 1.0 x 10 8 c. [OH ] = 1.0 x 10 2 d. [OH ] = 1.0 x 10 5 e. [H + ] = 2.0 x 10 3 f. [H + ] = 3.5 x 10 4 g. [OH ] = 7.50 x 10 7 h. [OH ] = 9.0 x 10 9 2. Determine the concentration of [H+] of each of the following. a. ph = 7.00 b. poh = 5.00 c. ph = 13.00 d. poh = 11.00 e. ph = 3.40 f. poh = 6.10 g. ph = 8.90 h. poh = 13.80 3. Determine the poh of the following if the ph is given a. ph = 5.40 b. ph = 8.60 c. ph = 2.90 d. ph = 12.60 4. Determine the concentration of the OH ions in solutions with the following ph values. a. ph = 4.10 b. ph = 5.10 c. ph = 1.60 d. ph = 9.20 5. Calculate ph of each of the following solutions. a. 0.0020 mol/l HCl b. 0.050 M NaOH c. 4.0 x 10 4 M Ba(OH) 2 d. 0.50 mol/l HNO 3 Answers a. 6.00 b. 8.00 c. 12.0 d. 9.00 e. 2.70 f. 3.46 g. 7.88 h. 5.95 a. 1e7 b. 1e9 c. 1e13 d. 1e3 e. 4e4 f. 1.3e8 g. 1.3e9 h. 0.63 a. 8.60 b. 5.40 c. 11.10 d. 1.40 a. 1.3e10 b. 1.3e9 c. 4e13 d. 1.6e5 a. 2.70 b. 12.70 c. 10.90 d. 0.30 9
ph practice 1) What is the ph and poh of a 1.2 x 10 3 M HBr solution? 2) What is the ph and poh of a 2.34 x 10 5 NaOH solution? 3) What is the ph and poh of a solution made by adding water to 15 grams of hydroiodic acid until the volume of the solution is 2500 ml? 4) What is the ph and poh of a solution that was made by adding 400 ml of water to 350 ml of 5.0 x 10 3 M NaOH solution? 5) What is the ph and poh of a solution with a volume of 5.4 L that contains 15 grams of hydrochloric acid and 25 grams of nitric acid? 6) A swimming pool has a volume of one million liters. How many grams of HCl would need to be added to that swimming pool to bring the ph down from 7 to 4? (Assume the volume of the HCl is negligible) ANSWER KEY 1. ph: 2.9 poh: 11.1 2. poh: 4.6 ph: 9.4 3. ph: 1.3 poh: 12.7 4. poh: 2.7 ph: 11.3 5. ph: 0.82 poh: 13.18 6. 3545 g 10
ANSWER THE FOLLOWING DISSOCIATION QUESTIONS: 1. Calculate the concentration of all species in a 0.70 mol/l HNO 3 solution. 2. Determine the [H 3 O + ] in 0.90 mol/l solution of weak acid H 2 S. (K a = 1.0 x 10 7 ) (3.0x 10 4 M) 3. Find the concentration of all species in a 0.10 M solution of NaOH. 4. Determine the concentration of all species in a 0.65 mol/l solution of an ammonia, if the base dissociation constant is 1.8 x 10 5. (3.4 x 10 3 M) 5. Find the [H + ] in a 0.86 M solution of the weak acid H 2 O 2. (Ka = 2.4 x 10 12 ) (1.4 x 10 6 M) 6. If [H 3 O + ] = 4.5 x 10 6 mol/l in a 0.45 mol/l solution of the weak acid HX, calculate percent dissociation. (0.001%) 7. Find the percent dissociation in 0.87 M solution of the weak base HPO 4 2 if K b is 1.6 x 10 7. (0.043%) 11
8. Calculate the [H + ] of a 0.38 mol/l weak acid that is dissociated 0.12%. (4.56 x 10 4 M) 9. Determine the K a for an acid, HA, if a 0.45 M solution is dissociated 0.025%. (2.8 x 10 8 ) 10. Calculate the the percent dissociation of a 0.60 mol/l aniline (C 6 H 5 NH 2 ) solution (Kb = 3.8 10 10 ) if it dissociates according to the following equation: (0.0025%) C 6 H 5 NH 2 + H 2 O C 6 H 5 NH 3 + + OH 11. Determine the Ka for an acid HA if a 0.750 mol/l solution is dissociated 0.015%. (1.7 x 10 8 ) 12. If [H 3 O + ] = 4.5 10 10 mol/l, calculate the Ka for a weak acid in a solution of 0.80 mol/l of an acid HB. (2.5 x 10 19 ) 13. Calculate the ph of a 0.10 mol/l solution of hypochlorous acid, HOCl (Ka = 3.5 10 8 ) (4.2) 12
14. A 0.20 mol/l solution of the weak base HPO 2 4 has a ph of 9.00. Find the Kb. (5.0 x 10 10 ) 15. Calculate the Ka of a weak acid, HX, if a 0.25 mol/l solution has a ph of 4.40. (6.3 x 10 9 ) 16. At 25 C, a 0.010 mol/l ammonia solution is 4.3% ionized. Calculate the poh and ph. (3.4, 10.6) 17. Hydrazine (N 2 H 4 ) is a weak base with a Kb of 3.0 10 6. The reaction of hydrazine in water is H 2 NNH 2 + H 2 O H 2 NNH 3 + + OH Calculate the the ph of a 2.0 mol/l solution of hydrazine. (11) 18. Calculate the percent dissociation of a 0.20 mol/l solution of the weak acid, HNO 2, if the ph of the solution is 4.20. (0.032%) 13
ANSWER THE FOLLOWING DISSOCIATION QUESTIONS: 1. Calculate the original concentration of the weak base, C 2 H 3 O 2 (acetate ion), if [OH ] = 1.5 x 10 5 and K b = 5.6 x 10 10. (0.4 M) 2. Calculate percent dissociation of a 0.60 M aniline (C 6 H 5 NH 2 ) solution (K b = 3.8 x 10 10 ) if it dissociates according to the following equation: (0.0025%) C 6 H 5 NH 2 + H 2 O C 6 H 5 NH 3 + + OH 3. Determine the K a for an acid HA if a 0.750 M solution is dissociated 0.015%. (1.7 x 10 8 ) 4. Compute the concentration of [OH ] in a 0.75 mol/l solution of Mg(OH) 2. 5. If [H 3 O + ] = 4.5 x 10 10 mol/l, calculate K a in a solution of 0.80 mol/l of an acid HB. (2.5 x 10 19 ) 6. Determine the concentration of all species plus the percent dissociation in a 0.60 mol/l ammonia solution. (K b = 1.8 x 10 5 ) (3.3 x 10 3 M, 3.3 x 10 3 M, 0.6 M, 0.55%) 7. Calculate the concentration of a solution of acetic acid (Ka = 1.8 x 10 5 ) with ph = 3.00. (0.056) 14
Are each of the following salts acidic, basic or neutral in water? Explain why. 1. Sodium sulfate 2. Potassium phosphate 3. Sodium nitrate 4. Sodium sulfide 5. Potassium chloride 6. Magnesium nitrate 7. Iron (III) Nitrate 8. Sodium carbonate 9. Potassium oxalate 10. Ammonium iodide 11. Potassium acetate 12. Chromium (III) bromide 13. Potassium dihydrogen phosphate 14. Sodium nitrite 15. Calcium oxide 15
ANSWER THE FOLLOWING NEUTRALIZATION QUESTIONS: 1. Write the complete reaction that occurs when the following acid and bases are reacted. a) Hydrochloric acid and sodium hydroxide. b) Sulfuric acid and potassium hydroxide. c) Nitric acid and calcium hydroxide. d) Phosphoric acid and lithium hydroxide. e) Sulfuric acid and aluminum hydroxide. 2. Calculate the concentration of a solution of KOH if 140.0 ml of the base is needed to neutralize 22.5 ml of 0.175 mol/l acid HNO 3. 3. Determine the volume of 0.750 mol/l LiOH required to neutralize 56.0 ml of 0.350 mol/l H 2 SO 4. 4. What volume of 0.240 mol/l H 2 SO 4 can be neutralized by 50.0 ml of 0.360 M NaOH? 5. Calculate the concentration of the acid, if 25.0 ml of H 3 PO 4 is required to neutralize 19.0 ml of 0.830 mol/l KOH. 6. What volume of 0.100 mol/l HCl is required to just neutralize 10.0 g of solid NaOH? 7. What volume of 0.250 mol/l nitric acid is needed to just neutralize 25.0 g of magnesium hydroxide? 8. What mass of calcium hydroxide is needed to just neutralize 250.0 ml of 0.100 mol/l HCl? Assume the volume does not change. 2. 0.0281 mol/l 3. 52.3 ml 4. 37.5 ml 5. 0.210 mol/l 6. 2.50 L 7. 3.43 L 8. 0.926 g 16
Titrations Worksheet 1. I titrated 3.5 ml of NaOH with 25 ml of 5.0 x 10 2 M HCl. Find the concentration of this base and determine its ph. (0.36 M, 13.6) 2. If it took me 25.4 ml of 5.0 mm HCl to titrate 50.0 ml of a strong basic solution with unknown concentration, what were the concentration and ph of the basic solution? (2.54 x 10 3 M, 11.4) 3. How many ml of 0.010 M NaOH will be required to neutralize 10.0 ml of HCl with a ph of 1.0? (100 ml) 17
ANSWER THE FOLLOWING QUESTIONS ON TITRATIONS: 1. A sample of vinegar is titrated with a 0.990 mol/l sodium hydroxide solution, to determine the concentration of acetic acid. Given the following data, a. Calculate the concentration of acetic acid in the vinegar for each trial. b. Calculate the average concentration over the three trials. (0.830 mol/l) 2. The neutralization of 0.900 g of an unknown monoprotic solid acid required 30.00 ml of 0.150 mol/l NaOH. Calculate the molar mass of the acid. (200 g/mol) 3. A sample of a monoprotic acid (molar mass 97.09 g/mol) is dissolved in enough water to make 250.0 ml of solution. A 12.00 ml aliquot of the acid solution is titrated with a 0.0850 mol/l solution of NaOH. If 17.55 ml is required to reach the endpoint, what is the mass of the original sample? (3.02 g) 18
4. Aspirin tablets are made of acetylsalicylic acid (ASA) and fillers. An Aspirin tablet with mass of 0.500 g was powdered, suspended in water and titrated with 0.150 mol/l NaOH solution. If it requires 11.80 ml of NaOH solution to reach the endpoint, how much ASA does the tablet contain? ASA is a monoprotic acid with a formula of C 9 H 8 O 4. (0.319 g) 5. A student pipetted 25.0 ml of an aqueous solution of an unknown monoprotic acid into an Erlenmeyer flask, added about 25 ml of water and titrated with a standard 0.0985 mol/l sodium hydroxide solution. The ph was measured after each addition. The graph below shows the graph obtained. Use the graph to answer the following questions. a. What was the concentration of the unknown acid? (0.104 mol/l) b. What would be a suitable range for an indicator to change colour for this titration? 19
Acids and Bases Review 1. Explain how the Lewis definition of a base is different from that of the Arrhenius definition of a base. Are Arrhenius bases also bases under the Lewis definition? Explain. 2. Determine the type of reaction occurring below. If possible label the conjugate acidbase pair in the appropriate place (Think about what is taking place in the reaction). a. H 2 SO 4 + H 2 O HSO 3 1 + H 3 O b. Ca(OH) 2 + 2 HNO 3 Ca(NO 3 ) 2 + 2 H 2 O c. NaCl Na + + Cl 3. What s the ph of a 3.3 x 10 5 M NaOH solution? 4. Find the ph of a 0.0050 M acetic acid solution. Ka = 1.8 x 10 5 (3.5) 5. What is the ph of a solution that contains 2.4 x 10 5 moles of hydrobromic acid in 0.50 L of water? (4.3) 20
6. What is the ph of a solution that contains 25 moles of nitric acid dissolved in 5000 L of water? (2.30) 7. In a few steps, describe how you would titrate a base of unknown concentration with an acid with concentration of 1 M. 8. I did a titration where it took 50 ml of 0.1 M hydrochloric acid to neutralize 500 ml of a base with unknown concentration. Using this information, what was the concentration of the base? (0.01 M) 9. I did a titration where it took 25 ml of 5 M NaOH to neutralize 1000 ml of an acid with unknown concentration. Using this information, what was the concentration of acid? (0.125 M) 10. If it takes 560 ml of 0.0050 M NaOH to neutralize 100.0 ml of H 2 SO 4 solution with unknown concentration, what was the original ph of the H 2 SO 4 solution? ( 1.9) 21